A testable scenario of WIMPZILLA with Dark Radiation

As the electromagnetic gauge symmetry makes the electron stable, a new abelian gauge symmetry may be responsible for the stability of superheavy dark matter. The gauge boson associated with the new gauge symmetry naturally plays the role of dark radiation and contributes to the effective number of `neutrino species', which has been recently measured by Planck. We estimate the contribution of dark radiation from the radiative decay of a scalar particle induced by the WIMPZILLA in the loop. The scalar particle may affect the invisible decay of the Higgs boson by the Higgs portal type coupling.Comment: 4 pages, 3 figure

Bounds on dark matter interpretation of Fermi-LAT GeV excess

Annihilation of light dark matter of $m_{\rm DM} \approx (10-40)$ GeV into the Standard Model fermions has been suggested as a possible origin of the gamma-ray excess at GeV energies in the Fermi-LAT data. In this paper, we examine possible model-independent signatures of such dark matter models in other experiments such as AMS-02, colliders, and cosmic microwave background (CMB) measurements. We point out that first generation of fermion final states is disfavored by the existing experimental data. Currently AMS-02 positron measurements provide stringent bounds on cross sections of dark matter annihilation into leptonic final states, and $e^+e^-$ final state is in severe tension with this constraint, if not ruled out. The $e^+e^-$ channel will be complementarily verified in an early stage of ILC and future CMB measurements. Light quark final states ($q\bar q$) are relatively strongly constrained by the LHC and dark matter direct detection experiments even though these bounds are model-dependent. Dark matter signals from annihilations into $q\bar{q}$ channels would be constrained by AMS-02 antiproton data which will be released in very near future. In optimistic case, diffuse radio emission from nearby galaxy (clusters) and the galactic center might provide another hint or limit on dark matter annihilation.Comment: 20 pages, 3 figures; figures and text updated, discussion improved, references added; updated to match published version in NP

An alternative interpretation for cosmic ray peaks

We propose an alternative mechanism based upon dark matter (DM) interpretation for anomalous peak signatures in cosmic ray measurements, assuming an extended dark sector with two DM species. This is contrasted with previous effort to explain various line-like cosmic-ray excesses in the context of DM models where the relevant DM candidate directly annihilates into Standard Model (SM) particles. The heavier DM is assumed to annihilate to an on-shell intermediate state. As the simplest choice, it decays directly into the lighter DM along with an unstable particle which in turn decays to a pair of SM states corresponding to the interesting cosmic anomaly. We show that a sharp continuum energy peak can be readily generated under the proposed DM scenario, depending on dark sector particle mass spectra. Remarkably, such a peak is robustly identified as half the mass of the unstable particle. Furthermore, other underlying mass parameters are analytically related to the shape of energy spectrum. We apply this idea to the two well-known line excesses in the cosmic photon spectrum: 130 GeV gamma-ray line and 3.5 keV X-ray line. Each observed peak spectrum is well-reproduced by theoretical expectation predicated upon our suggested mechanism, and moreover, our resulting best fits provide rather improved chi-square values.Comment: 9 pages, 3 figure

Hidden-sector-assisted 125 GeV Higgs boson

In order to significantly raise the mass of the supersymmetry Higgs boson, we consider a radiative correction to it by heavy (\sim 1 TeV) hidden sector fields, which communicate with the Higgs through relatively heavy "messengers" (300-500 GeV). The messenger fields (S, \bar{S}) are coupled to the Higgs ("y_HSH_uH_d," y_H\lesssim 0.7) and also to hidden sector fields with a Yukawa coupling of order unity. The hidden sector fields are assumed to be large representations of a hidden gauge group, and so their scalar partner masses can be heavier than other typical soft scalars in the visible sector. Even with a relatively small y_H (\sim 0.2) or tan\beta\sim 10 but without top-stop's considerable contributions, the radiative correction by such hidden sector fields can be enhanced enough to yield the 125 GeV Higgs mass.Comment: 5 pages, 3 eps figure

Electro-Weak Dark Matter: non-perturbative effect confronting indirect detections

We update indirect constraints on Electro-Weak Dark Matter (EWDM) considering the Sommerfeld-Ramsauer-Townsend (SRT) effect for its annihilations into a pair of standard model gauge bosons assuming that EWDM accounts for the observed dark matter (DM) relic density for a given DM mass and mass gaps among the multiplet components. For the radiative or smaller mass splitting, the hypercharged triplet and higher multiplet EWDMs are ruled out up to the DM mass ~ 10 - 20 TeV by the combination of the most recent data from AMS-02 (antiproton), Fermi-LAT (gamma-ray), and HESS (gamma-line). The Majorana triplet (wino-like) EWDM can evade all the indirect constraints only around Ramsauer-Townsend dips which can occur for a tiny mass splitting of order 10 MeV or less. In the case of the doublet (Higgsino-like) EWDM, a wide range of its mass > 500 GeV is allowed except Sommerfeld peak regions. Such a stringent limit on the triplet DM can be evaded by employing a larger mass gap of the order of 10 GeV which allows its mass larger than about 1 TeV. However, the future CTA experiment will be able to cover most of the unconstrained parameter space.Comment: 17 pages, 4 figures; result for an O(10 GeV) mass gap, future sensitivity of CTA, and references adde

Galactic center GeV gamma-ray excess from dark matter with gauged lepton numbers

The recently observed excess in gamma-ray signal near the Galactic center suggests that dark matter particles may annihilate into charged fermions that produce gamma-ray to be observed. In this paper, we consider a leptonic dark matter, which annihilates into the standard model leptons, $\mu^+ \mu^-$ and $\tau^+ \tau^-$, by the interaction of the gauged lepton number ${\rm U(1)}_{L_\mu-L_\tau}$ and fits the observed excess. Interestingly, the necessary annihilation cross section for the observed gamma-ray flux provides a good fit to the value for the relic abundance of dark matter. We identify the preferred parameter space of the model after taking the existing experimental constraints from the precision measurements including the muon $(g-2)$, tau decay, neutrino trident production, dark matter direct detection, LHC, and LEP experiments.Comment: 18 pages, 8 figures, references added, matches published versio

A study on the oversight scheme over recognized organizations under the international instruments

This dissertation is a study on the oversight scheme over recognized organizations acting on behalf of flag States for consistent and effective implementation of international instruments. A brief history of classification societies, which account for the most recognized organizations, is dealt with and the concept of recognized organizations and their significance is looked into in the first stage. The legal background of delegation of flag States’ authority to recognized organizations is examined, categorized by legal instruments developed by IMO and ILO. Categories of recognized organizations are identified through consideration of their capability and performance aspects. Consolidated audit summary reports (CASR) under the VIMSAS are investigated to justify the need for oversight of recognized organizations and to figure out specific problematic areas to be improved. Results of Port State Control (PSC) in Paris MoU are examined to look into the extent of recognized organization (RO)’s attribution to non-conformity with IMO instruments and to investigate differentials of performance level between various recognized organizations. The Qualification Management System Certification Scheme (QSCS) of International Association of Classification Societies (IACS) is investigated especially focusing on Accredited Certification Body (ACB). EU’s monitoring system of quality management systems of is recognized organizations is investigated. iv The Maritime Labour Convention 2006 developed by The International Labour Organization (ILO) is investigated in terms of its survey and certification scheme and delegation of States’ authority to recognized organizations to examine the applicability of RO related instruments developed by IMO in MLC 2006. The concluding chapter examines the areas to be improved for more effective implementation of international instruments in terms of oversight of recognized organizations based on the research in the previous chapter. A number of recommendations are made with regard to an effective oversight scheme of recognized organizations

Searching for Boosted Dark Matter via Dark-Strahlung

We propose a new search channel for boosted dark matter (BDM) signals coming from the present universe, which are distinct from simple neutrino signals including those coming from the decay or pair-annihilation of dark matter. The signal process is initiated by the scattering of high-energetic BDM off either an electron or a nucleon. If the dark matter is dark-sector U(1)-charged, the scattered BDM may radiate a dark gauge boson (called "dark-strahlung") which subsequently decays to a Standard Model fermion pair. We point out that the existence of this channel may allow for the interpretation that the associated signal stems from BDM, not from the dark-matter-origin neutrinos. Although the dark-strahlung process is generally subleading compared to the lowest-order simple elastic scattering of BDM, we find that the BDM with a significant boost factor may induce an O(10-20%) event rate in the parameter regions unreachable by typical beam-produced dark-matter. We further find that the dark-strahlung channel may even outperform the leading-order channel in the search for BDM, especially when the latter is plagued by substantial background contamination. We argue that cosmogenic BDM searches readily fall in such a case, hence taking full advantage of dark-strahlung. As a practical application, experimental sensitivities expected in the leading-order and dark-strahlung channels are contrasted in dark gauge boson parameter space, under the environment of DUNE far-detectors, revealing usefulness of dark-strahlung.Comment: 9 pages, 4 figures, Journal-submitted versio